Amorphous materials substantially lack any long range atomic order and are characterized by X-ray diffraction patterns consisting of diffuse (broad) intensity maxima, quantitatively similar to the diffraction patterns observed for liquids or inorganic oxide glasses. Such patterns are in stark contrast to those observed with crystalline materials: diffraction patterns which consist of sharp, narrow intensity maxima.
Amorphous materials exist in a metastable state. Thus, upon heating to a sufficiently high temperature, they begin to crystallize with evolution of the heat of crystallization; the X-ray diffraction pattern thereby begins to change from that observed for amorphous materials to that observed for crystalline materials.
The most well-known disclosure directed to amorphous metallic alloys is U.S. Pat. No. 3,856,513 to H. S. Chen and D. E. Polk. Disclosed therein is a class of amorphous metallic alloys having the formula M.sub.a Y.sub.b Z.sub.c, where M is at least one metal selected from the group of iron, nickel, cobalt, chromium and vanadium, Y is at least one element selected from the group consisting of phosphorus, boron and carbon, Z is at least one element selected from the group consisting of aluminum, antimony, beryllium, germanium, indium, tin and silicon, "a" ranges from about 60 to 90 atom percent, "b" ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to 15 atom percent.
With continuing research and development in the area of amorphous metallic alloys, it has become apparent that certain alloy systems possess magnetic and physical properties which enhance their utility in certain applications, particularly in electrical applications as core materials for transformers, generators and electric motors. One such alloy which, early on, was identified as exhibiting such properties is Fe.sub.80 B.sub.20.
It is known, however, that Fe.sub.80 B.sub.20 is difficult to cast in the amorphous form and tends to be thermally unstable. Thus, alloys of greater stability and castability had to be developed to allow the practical use of amorphous metal alloys in the manufacture of electromagnetic cores, especially cores for transformers. One such class of alloys is disclosed in U.S. Pat. No. 4,219,355.
The alloys disclosed in U.S. Pat. No. 4,219,355 are represented by the formula Fe.sub.a B.sub.b Si.sub.c C.sub.d wherein "a", "b", "c" and "d" are in atomic percentages and range from about 80 to about 82, about 12.5 to about 14.5, about 2.5 to about 5, and about 1.5 to about 2.5, respectively. These alloys exhibit improved AC and DC magnetic properties that remain stable at temperatures up to about 150.degree. C. As a result, these alloys are particularly suitable for use in power transformers, aircraft transformers, current transformers, 400 Hz transformers, magnetic switch cores, high gain magnetic amplifiers and low frequency inverters.
Other classes of alloys have been identified as being suitable for use in the manufacture of transformers. For example, U.S. Pat. Nos. 4,217,135 and 4,300,950 are directed to certain iron-boron-silicon alloys which are disclosed as being useful in the manufacture of transformer cores.
As is readily apparent from the disclosures in the above referenced patents, it is well-recognized that differences in chemical compositions need not be great in order to achieve dramatic effects on the castability of amorphous metallic alloys, the resultant magnetic and mechanical properties, and the thermal stablitiy of these properties. For transformer core materials in particular, ease of castability, high saturation magnetization, low core loss, low exciting power, ductility and high thermal stability are the most desirable properties.
Although substantial progress has been made in identifying alloys which more closely meet the needs of transformer core manufacturing industry, additional developments toward yet even higher saturation induction, lower core loss, lower exciting power and better thermal stability at elevated operating temperatures are necessary.